I think the most important feature is to have a checkbox on the user edit form for Active/Inactive. E-mail notifications or confirmation messages are not as important, but right now if we register someone as inactive, there's no way for the administrator to activate them.
I believe what you're describing by having confirmation e-mails to validate a person's e-mail address, that's great and a lot of websites have it. It would be a nice feature for Sitefinity, but not as vital to being able to set someone's active status in the admin area.
Thanks for keeping Sitefinity the best CMS around!